Drill bit, drill kit and method for drilling a cavity or a recess into a skull

ABSTRACT

A drill bit for drilling a cavity or a recess into a skull, wherein the cavity or the recess is configured to receive an implantable fixture screw unit of a hearing aid system, is disclosed. The drill bit includes a first part including a drill tip with a first drill diameter, wherein the drill tip comprises a tip angle of between 137 degrees to 143 degrees along a longitudinal axis of the drill bit and wherein the drill tip comprises a back rake angle of between −1 degree and +1 degree, in particular a back rake angle of substantially 0 degrees, a second part including a plurality of flute blades with a second drill diameter, wherein the second drill diameter is greater that the first drill diameter, and a transition part which is arranged between the first part and the second part and along the longitudinal axis, wherein the transition part includes a body clearance.

FIELD OF THE DISCLOSURE

The present disclosure relates to the field of drill bits, drill kitsand methods for drilling. More particularly, the disclosure relates to adrill bit, a drill kit and a method for drilling a cavity or a recessinto a skull, wherein the cavity or the recess is configured to receivean implantable fixture screw unit of a hearing aid system.

BACKGROUND

Medical implants such as bone anchored hearing aid systems are appliedfor the rehabilitation of patients suffering from hearing losses forwhich traditional hearing aids are insufficient. A typical bone anchoredhearing aid system comprises an external hearing aid provided with avibrating transducer connected to a skin-penetrating abutment through acoupling. The abutment may have an interconnection to an implantablefixture screw unit anchored in the skull bone. The implantable fixtureis typically made of titanium and may be provided with a flange toprevent the fixture from being pushed through the skull bone whenexposed to a sudden accidental impact.

The abutment penetrates the skin and the subcutaneous tissue in order toestablish a direct coupling (direct bone conduction) from a hearing aidprocessor to the skull bone.

The methods for installing bone anchored hearing aid implant systems aremoving towards minimally invasive methods that can be performed quicklyin order to minimize intra- and post-operative problems, to achieve apredictable outcome, and to achieve better cosmetic results.

However, the existing incision techniques are rather complicated andrequire a flap area to be provided by making an incision. Typically, ascalpel is used to make an incision down to the periosteum along amarking of the incision area and to separate the tissue from theunderlying periosteum. Further, all subcutaneous tissue in the graftarea is separated from the periosteum. Additionally, the subcutaneoustissue needs to be carefully separated from the skin graft, and all hairfollicles need to be removed. Furthermore, some level of manual skinthinning typically is required to be performed.

Some attempts have been made to avoid the linear incision techniques toinstall implants for bone anchored hearing aids. Some of these attemptsinclude punch techniques. The techniques apply a standard biopsy punchthat is used to provide a circular incision of 5-12 mm.

These techniques are associated with a number of drawbacks. Thesedrawbacks include the risk of damaging the tissue due to friction, heatand tearing caused by the action of the drill.

The punching techniques apply punching holes larger than 5 mm in orderto allow for introducing irrigation fluid (to cool the bone tissue)during the drilling process and also for providing sufficientvisibility. These large punch diameters are not optimal for the softtissue abutment interface. A large circular incision will prolong thehealing time and introduce the risk of granulation tissue formation andsubsequent infection. Moreover, the skin thickness needs to bedetermined pre- and/or intra-operatively.

Additionally, it is known to use a minimally invasive Ponto surgerytechnique in order to install implants for bone anchored hearing aids.Hereby, an incision hole is made by using a biopsy punch. Afterwards theperiosteum and soft tissue are removed from the transplantation site.The drilling procedure comprises two different drilling steps. A firstdrill is used in order to generate a first cavity or recess. Afterwards,a widening drill is used in order to widen the first cavity or recessand to prepare the cavity or recess for the implant for bone anchoredhearing aids. By using different drills, the operation surgery time isprolonged and the switching, restarting and realigning of the wideningdrill may cause adverse consequences for the cavity or recess to bedrilled.

Therefore, there is a need to provide a solution that addresses at leastsome of the above-mentioned problems.

SUMMARY

According to a first exemplary aspect a drill bit for drilling a cavityor a recess into a skull is disclosed. The drill bit may comprise afirst part including a drill tip with a first drill diameter, whereinthe drill tip comprises a tip angle of between 137 degrees to 143degrees along a longitudinal axis of the drill bit. A tip angle ofbetween 137 degrees to 143 degrees is advantageous for drilling into therelatively hard skull material. The tip angle of between 137 degrees and143 degrees enables a sufficient engagement of the cutting lips of thedrill tip with the skull material. The first part of the drill bit isthe part of the drill bit which is closest to the bone during drilling.The drill tip may include a pointed end interfacing with the bone.Although the term pointed is used, the term pointed includes any knownstructure, interfacing with the bone at the start of drilling, thatfacilitates piercing of the bone for creation of a preliminary hole. Thedrill tip may comprise a back rake angle of between −1 degree and +1degree, in particular a back rake angle of substantially 0 degrees. Theback rake angle describes the angle of the cutting face of the drill tiprelative to the skull. A negative back rake angle of the drill tip leadsto a slightly duller cutting edge design. Hereby, the tactile feedbackwhile feeding the drill may be increased. Zero rake angle or a positiverake angle leads to a sharper and more pointed drill bit. Thus, cuttingforces and power requirements for the drill step may be reduced. Thelength along the longitudinal axis of the first part may be less thanthe length along the longitudinal axis of the second part.

The drill bit may further comprise a second part including a pluralityof flute blades with a second drill diameter, wherein the second drilldiameter is greater than the first drill diameter. By providing a drillbit comprising a first drill diameter and a second drill diameter,wherein the second drill diameter is greater than the first drilldiameter, a cavity or a recess for an implantable fixture screw unit ofa hearing aid system may be drilled into the skull in one drill step.Hereby, the final osteotomy for an implant may be performed in one step.The drill diameter of the first or the second part of the drill tip maybe defined as the maximum diameter along the longitudinal axis of thefirst or the second part of the drill bit.

The drill bit may further comprise a transition part which is arrangedbetween the first part and the second part and along the longitudinalaxis, wherein the transition part includes a body clearance.

According to another aspect, a drill kit comprising a drill bitaccording to the first exemplary aspect and further comprising a guidingtool is disclosed. The guiding tool may comprise a hollow tube, whereinthe diameter of the hollow tube is greater than the second drilldiameter. Hereby, the soft tissue may be protected from the drill bit.Additionally, saline or a coolant may be filled in the guiding tool inorder to cool during the drilling process. The guiding tool may act as ahard stop for the drilling bit, so that the drill depth can becontrolled.

According to yet another aspect, a method for drilling a cavity or arecess into a skull, wherein the cavity or the recess is configured toreceive an implantable fixture screw unit of a hearing aid system, isdisclosed. The method may comprise applying an incision hole to a bonelayer of the skull by using a first tool. The incision hole may beapplied by the usage of a punching tool in order to make the incisionhole.

The method may further comprise cleaning the incision hole by using acleaning tool. The step cleaning the cavity or the recess mayadditionally comprise the removal of the periosteum and soft tissue. Themethod may further comprise arranging a guiding tool into the cleanedcavity or recess, wherein the guiding tool includes a hollow tube. Themethod may further comprise applying the drill bit into the hollow tubeand drilling the cavity or the recess in a single step. The stepdrilling the cavity or the recess in a single step may be performedwithout switching the drill bits. The cavity or the recess has adiameter and depth matching the dimensions of the implant so that theimplant may be screwed into the cavity or recess. In an embodiment, theimplant includes an implant of a bone anchored hearing aid.

In the following, further exemplary features of all aspects of thepresent invention will be described in more detail.

A hearing aid system may generally be understood or include a hearingaid (which may also be termed a hearing device, a hearing instrument ora hearing assistance device) that is adapted to improve or augment thehearing capability of a user by receiving an acoustic signal from auser's surroundings, generating a corresponding audio signal, possiblymodifying the audio signal and providing the possibly modified audiosignal as an audible signal to at least one of the user's ears.‘Improving or augmenting the hearing capability of a user’ may includecompensating for an individual user's specific hearing loss. The“hearing aid” may further refer to a device such as a hearable, anearphone or a headset adapted to receive an audio signal electronically,possibly modifying the audio signal and providing the possibly modifiedaudio signals as an audible signal to at least one of the user's ears.Such audible signals may be provided in the form of an acoustic signalradiated into the user's outer ear, or an acoustic signal transferred asmechanical vibrations to the user's inner ears through bone structure ofthe user's head and/or through parts of the middle ear of the user orelectric signals transferred directly or indirectly to the cochlearnerve and/or to the auditory cortex of the user.

The hearing aid of the hearing system is adapted to be worn in any knownway. This may include arranging a unit of the hearing aid attached to afixture implanted into the skull bone such as in a Bone Anchored HearingAid or arranging a unit of the hearing aid as an entirely or partlyimplanted unit such as in a Bone Anchored Hearing Aid. The hearing aidmay be implemented in one single unit (housing) or in a number of unitsindividually connected to each other.

In an embodiment of the disclosure, each of the plurality of fluteblades of the second part of the drill bit may comprise at least oneland, wherein the second part comprises parabolic or essentiallyparallel, in particular cross-section defining, opposing surfacesextending between the lands of the plurality of flute blades. The landof a flute blade may be defined as the outer portion of the flute bladebetween two adjacent flutes. The parabolic or essentially parallelsurfaces of the second part leads to an improved bone chip extraction.Additionally, the total drill work can be reduced so that an efficientremoval of bone volume can be provided.

The plurality of the flute blades of the second part may comprise acutting edge with a thickness of between 0.10 mm to 0.40 mm. Saidcutting edge thickness of the plurality of flute blade is beneficial forthe cutting efficiency of the drill bit.

A pair of adjacent flute blades may define drill flutes between adjacentflute blades, wherein the thickness of the drill flutes or the fluteblades may vary along the drill bit, in particular along thelongitudinal axis of the drill bit. This allows for optimizing thethickness distribution of the drill bit regarding the force and torqueof the drill bit. The thickness of the drill flutes may vary between 0.8mm and 1.2 mm.

The second part of the drill bit may include at least two flute bladessuch as two or three or four or more flute blades along the longitudinalaxis of the drill bit.

The second part or the transition part of the drill bit may include aback-rake angle which is either positive or negative. The back rakeangle describes the angle of a cutting face relative to a workpiece(e.g. to the skull). A negative back rake angle of the second part orthe transition part leads to an increase of tactile feedback whilefeeding the drill. A positive rake angle leads to a reduction of cuttingforces and power requirements. The back rake angle of the flute bladesmay be within an angle range of between −3 degrees to +3 degrees notincluding 0 degrees.

The second part of the drill bit may include a helix angle between thelongitudinal axis and a direction of the flute blades, in particular aplane of the flute blades, of between 20 degrees to 30 degrees, inparticular a helix angle of between 24 degrees and 26 degrees. Thesecond part of the drill bit may also include a helix angle of 25degrees between the longitudinal axis and the direction of the fluteblades along the longitudinal axis. Aforementioned helix angles lead toan increased bone chip removal and are beneficial for the feed rate ofthe drill bit.

The transition part of the drill bit may include a region with constantdiameter along the longitudinal axis. The length of the region withconstant diameter along the longitudinal axis may be between 1.05 mm and1.55 mm. Preferably, the region of constant diameter does not have acutting edge.

The body clearance of the transition part of the drill bit may include aminimum diameter equal to a diameter of the first part, preferably to aminimum diameter of the first part, and a maximum diameter equal to adiameter of the second part. Hereby, a smooth transition between thefirst part of the drill bit and the second part of the drill bit may beprovided.

The body clearance of the transition part may include a transition angleof 7 degrees to 13 degrees along the longitudinal axis and between aminimum diameter and a maximum diameter of the transition part. Thetransition angle may be defined as the angle between the planeperpendicular to the longitudinal axis of the drill bit and the bodyclearance of the transition part of the drill bit. Said transition angleis beneficial for providing a cavity or a recess in a skull with onedrill bit in one drilling step.

A first length along the longitudinal axis and between the end of thedrill tip and the maximum diameter of the transition part may be between4.65 mm and 4.75 mm. The drill bit may have a first drill diameterbetween 3.78 mm and 3.82 mm.

The drill tip may include a cutting edge angle of 7 degrees to 13degrees. The cutting edge angle may be defined as an angle formed by aflank of the drill tip and a plane perpendicular to the longitudinalaxis. Said cutting edge angle provides beneficial strength and rigidityto the cutting edge. The cutting edge angle may also be defined as theclearance angle of the drill tip.

The drill tip may comprise a web thickness of between 0.20 mm to 0.30mm, especially of between 0.24 mm to 0.26 mm. The web thickness is thethickness of the drill tip in a plane perpendicular to the longitudinalaxis. The aforementioned web thickness may be beneficial regarding theneeded thrust to apply to the drill bit in order to penetrate the skull.

The guiding tool may protect the soft tissue during drilling, ensuringthat the correct drilling depth is obtained (thus preventing too deeprecesses or cavities) and contributing to adequate flushing. Inaddition, the guiding tool may ensure that the recess or cavity is madeperpendicular to the bone and/or skin surface.

The guiding tool or the hollow tube of the guiding tool may comprise anexternal thread for fixating the guiding tool into the operational siteby screwing the guiding tool into the soft tissue.

The thickness of the hollow tube of the guiding tool may vary in orderto provide support for the drill bit and also in order to provide roomfor irrigation or for a coolant inside the hollow tube. The hollow tubeof the guiding tool may comprise one upper part comprising a first innerdiameter, one lower part comprising a second inner diameter and onemiddle part located between the upper and the lower part. The innerdiameter of the middle part may be variable in order to connect theupper part to the lower part. The first inner diameter may be greaterthan the second inner diameter. Also, the first inner diameter may besmaller than the second inner diameter.

The guiding tool may comprise a hollow channel connected to the hollowtube in order to provide a coolant or saline to the bottom of theosteotomy. The hollow channel may be arranged essentially perpendicularto the hollow tube for the drill bit. The guiding tool may also comprisea plurality of hollow channels and/or gaps in order to enable thetransportation of bone debris out of the guiding tool. The hollowchannel and/or the gaps for the bone debris may be located in the upperpart of the guiding tool, so that during the drilling process softtissue does not cover the channels and/or gaps.

The drill bit may comprise a region with an extended diameter whichcontacts a hard stop of the guiding tool when a predetermined drillingdepth is reached. Hereby, idling of the drilling bit can be prohibitedwhen the bottom of the osteotomy is reached.

The guiding tool may be connected to the drill bit, wherein the guidingtool and the drill bit are connected in such a way that the guiding toolis not rotating with the drill bit in order to protect the soft tissue.The guiding tool and the drill bit may also be connected in such a waythat that the guiding tool rotates with the drill bit. The drill depthmay be controlled by a resilient tube mechanism integrated in the lowerpart of the hollow tube.

A punch may be integrated into the bottom part of the hollow tube of theguiding tool, so that the incision hole in the bone layer of a skull maybe also provided by using the drilling kit.

The drill bit may be connected and/or coupled to the hand piece of thedrill through a spring mechanism. When a force is applied to the drillbit, for example when the drill bit is pressed against the skull duringdrilling, the spring connection may be activated and the hand piece maybe enabled to drive the drill bit. When no force is applied to thedrill, the spring connection may separate the drill bit from the handpiece and the drill bit stops to rotate. Hereby, a rotation of the drillbit when drilling through the skull bone can be prevented.

The spring mechanism may comprise a spring coupling, wherein the springcoupling may comprise at least two spring elements. The spring elementsmay be arranged to each other in a horizontal plane or in a verticalplane.

The incision hole may be provided in a soft tissue by pressuring a sharpblade of a cylindrical hollow punch member through the soft tissue. Thismay be followed by pulling out the cylindrical hollow punch member andremoving the punched out soft tissue from the incision hole.

The implantable fixture screw unit may be configured to receive a boneconduction hearing aid system. The implantable fixture screw unit maycomprise an elongated part where a first end of the elongated part isthreaded and configured to be anchored in the skull bone of therecipient via the drilled cavity or the recess in the skull. Theelongated part may comprise a second end configured to receive a skinabutment unit configured to receive the bone conduction hearing aidsystem. The variation in skin thickness in patients is addressed by theskin abutment unit of different lengths. An outer surface of theelongated part may be modified by laser ablation for the purpose ofroughen the outer surface and obtaining an improved osseointegration ofthe implantable fixture screw unit.

Where an unthreaded part of the elongated part may have a length withina range of 3 mm to 12 mm, 3 mm to 9 mm or 3 mm to 8 mm. The length ofthe unthreaded part of the elongated part may be orthogonal to theskull. The length may be adapted to the thickness of the soft tissue onthe skull of the patient.

The skin abutment unit may have a thickness orthogonal to the skull ofbetween 3 mm to 12 mm, 3 mm to 9 mm or 3 mm to 8 mm.

The skin abutment unit may be attached to the elongated part by screwingit on to the elongated part or by a snap coupling where the skinabutment unit is pressed on to the elongated part by a movement along anaxis orthogonal to the skull.

The implantable fixture screw unit may be made of memory metal, such asNitinol, or an alloy of one or more of following combinations: Ag—Cd,Au—Cd, Cu—Al—Ni, Cu—Sn; Cu—Zn, Cu—Zn—(Si,Sn,Al), In—Ti, Ni—Al, Ni—Ti,Fe—Pt, and Mn—C

The skin abutment unit may be formed in one piece with the elongatedpart.

A diameter of the unthreaded part of the elongated part is smaller thana diameter of the threaded elongated part. The diameter of theunthreaded part of the elongated part is smaller than a diameter of theskin abutment unit.

The unthreaded elongated part may be manufactured from an elasticmaterial, such as NiTi alloy, super-elastic polymer or super elasticceramics. However, the disadvantages of utilizing such materials are asfollowing:

-   -   Forces that are excerted on the elongated part during use or        trauma will not be transferred fully to the implant but rather        results in bending of the elongated part.    -   A super-elastic material, such as NiTi alloy, has an e-modulus        and stress-strain behavior that is more similar to tissue        compared with titanium or steel. Action such as scratching the        head, chewing, turning the head and talking will result in        movements of the soft tissue around the abutment, generating        interfacial stresses around the abutment.

The disadvantages of having a flexible implantable fixture screw unitcan be reduced by decreasing the diameter and/or the length of theimplantable fixture screw, for example the elongated part. By reducingthe diameter of the flexible implantable fixture screw provides anotherchallenge such as how to connect a bone conduction hearing device on tothe implantable fixture screw unit.

To solve the problem of reduced diameter the implantable fixture screwunit may include two or more of the elongated parts, where theunthreaded part of the elongated part is made of the elastic material,such as NiTi alloy, super-elastic polymer or super elastic ceramics. Inthis example, the diameter of the unthreaded part of the elongated partis smaller than a diameter of the threaded elongated part. The diameterof the unthreaded part of the elongated part is smaller than a diameterof the skin abutment unit.

The bone conduction hearing aid system may be configured to be connectedto the two or more elongated parts either directly or via an adapterunit. The adapter unit is configured to interconnect the two or moreelongated parts on a first surface of the adapter unit and to connect tothe bone conduction hearing aid system on a second surface of theadapter unit, and wherein the first surface is opposite to the secondsurface. Instead of having a skin abutment unit connected to each of thetwo or more elongated parts, it would be of an advantage to interconnectthe two or more elongated parts with the adapter unit and without theskin abutment units being connected to the two or more elongated parts.Thereby, the distance from the skin surface to the bone conductionhearing aid system applied onto the implantable fixture screw unit isreduced.

The shape of the two or more elongated parts may be straight. In anotherexample, the two or more elongated parts may be trapeze shaped ortapered resulting in a smaller diameter at the first end of theelongated part where the skin abutment unit is applied or the adapterunit. The tapered shape and the trapeze shape is beneficial in terms ofstability since only a limited part (near the first end) of theelongated part is bending/flexible when subjected to lateral force fromthe bone conduction hearing aid system.

The elongated part may have a diameter that varies according to aprofile along the length, wherein the profile may be a trapeze profile,tapered profile, or an hour-glass profile.

Aforementioned features shall be considered to be disclosed in anycombination with each other. Further, the disclosure of any means forperforming a method step shall be understood to also disclose therespective method step and the disclosure of a method step shall beunderstood to also disclose respective means for performing the step.

BRIEF DESCRIPTION OF DRAWINGS

The aspects of the disclosure may be best understood from the followingdetailed description taken in conjunction with the accompanying figures.The figures are schematic and simplified for clarity, and they just showdetails to improve the understanding of the claims, while other detailsare left out. Throughout, the same reference numerals are used foridentical or corresponding parts. The individual features of each aspectmay each be combined with any or all features of the other aspects.These and other aspects, features and/or technical effect will beapparent from and elucidated with reference to the illustrationsdescribed hereinafter in which:

FIG. 1 schematically shows a perspective view of a drilling bitaccording to an embodiment of the disclosure;

FIG. 2 schematically shows a detail view of the embodiment shown in FIG.1;

FIG. 3 schematically shows the cross sectional view A-A from FIG. 2;

FIG. 4 schematically shows a side view of the embodiment shown in FIG.1;

FIG. 5A schematically shows a cavity or a recess drilled with two drillbits according to the state of the art;

FIG. 5B schematically shows a cavity or a recess drilled with one drillbit according to an embodiment of the disclosure;

FIG. 6 schematically illustrates a guiding tool according to anembodiment of the disclosure in a perspective view;

FIG. 7 schematically shows a cross sectional view of a guiding toolaccording to an embodiment of the disclosure;

FIG. 8 schematically shows a guiding tool according to an embodiment ofthe disclosure in a front view; and

FIGS. 9A-9C illustrate examples of an implantable fixture screw unit;

FIGS. 10A-10B illustrate examples of an implantable fixture screw unit;and

FIGS. 11A-11C illustrate examples of an implantable fixture screw unitand an adapter unit.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations. Thedetailed description includes specific details for the purpose ofproviding a thorough understanding of various concepts. However, it willbe apparent to those skilled in the art that these concepts may bepracticed without these specific details. Several aspects of theapparatus and methods are described by various blocks, functional units,modules, components, circuits, steps, processes, algorithms, etc.(collectively referred to as “elements”). Depending upon particularapplication, design constraints or other reasons, these elements may beimplemented using electronic hardware, computer program, or anycombination thereof.

Now referring to FIG. 1, which illustrates a perspective view of a drillbit 2 for drilling a cavity or a recess into a skull according to anembodiment of the disclosure. The drill bit 2 comprises a first part 4,a transition part 6 and a second part 8. The transition part 6 isarranged between the first part 4 and the second part 8. The drill bit 2comprises a shank 10 in order to connect the drill bit 2 to a handpiece. Between the second part 8 and the shank 10 a circumferentialflange 12 is arranged.

The first length of the first part 4 of the drill bit 2 is less than thesecond length of the second part 8 of the drill bit 2. The length(l_(l)) along the longitudinal axis (X) and between the end of the drilltip (14) and a maximum diameter of the transition part (6) may bebetween 4.65 mm and 4.75 mm.

As show in FIG. 2, the first part 4 of the drill bit 2 comprises a drilltip 14 with a tip angle α of between 137 degrees and 143 degrees along alongitudinal axis X of the drill bit 2. The first part 4 of the drillbit 2 is the part of the drill bit 2 which is closest to the bone duringdrilling.

The first part 4 further comprises a first drill diameter d₁, whereinthe drill diameter d₁ is bordering flanks 16 of the drill tip 14. Thedrill tip 14 may have a first drill diameter d₁ between 3.78 mm and 3.82mm. The second part 8 may have a second drill diameter d₂, wherein thesecond drill diameter d₂ is greater than the first drill diameter d₁. Byproviding a drill bit 2 comprising a first drill diameter d₁ and asecond drill diameter d₂, wherein the second drill diameter d₂ isgreater than the first drill diameter d₁, a cavity or a recess for animplantable fixture screw unit of a hearing aid system may be drilledinto the skull in one drill step. Hereby, the final osteotomy for animplant may be performed in one step.

The first part 4 of the drill bit 2 further comprises a cutting edgeangle β. As shown in FIG. 3, the cutting edge angle β may be defined asan angle formed by a flank 16 of the drill tip and a plane perpendicularto the longitudinal axis X. The cutting angle may lie between 7 degreesand 13 degrees.

The drill tip 14 of the drill bit 2 comprises a back rake angle ofsubstantially 0 degrees. The back rake angle of substantially 0 degreesleads to a sharp drill tip 14 whereby cutting forces and powerrequirements for the drill step may be reduced.

The transition part 6 includes a region 18 with an essentially constantdiameter along the longitudinal axis X. The length l_(r) of the region18 is between 1.05 mm and 1.55 mm and the region 18 may not comprise acutting edge. The transition part 6 may further comprise a bodyclearance 20, wherein the body clearance 20 comprises a transition angleγ of 7 degrees to 13 degrees. The transition angle γ is defined as theangle between a plane perpendicular to the longitudinal axis X of thedrill bit 2 and the body clearance 20 of the transition part 6 of thedrill bit 2. Aforementioned transition angle γ is beneficial forproviding a cavity or a recess in a skull with one drill bit 2 in onedrilling step.

FIG. 4 illustrates a side view of the embodiment shown in FIG. 1. Asshown in FIG. 4, the second part 8 of the drill bit 2 comprises twoflute blades 22 with the second drill diameter dz. Because of the drilldiameter d₂ being greater than the drill diameter d₁ a cavity or arecess for an implantable fixture screw unit of a hearing aid system maybe drilled into the skull in one drill step in a beneficial way.

The flute blades 22 each comprise one land 24. The land 24 may bedefined as the outer portion of the body of the second part 8 borderingthe flute blades 22. Between the two flute blades 22 two flutes 26 arearranged. The opposing surfaces of the flute blades 22 which extendbetween the lands 24 of the flute blades 22 may comprise a parabolic oran essentially parallel cross-section. The parabolic or essentiallyparallel surfaces of the flute blades 22 or flutes 26 lead to animproved bone chip extraction. Additionally, the total drill work of thedrill bit 2 may be reduced so that an efficient removal of bone volumecan be provided.

Each of the flute blades 22 comprises a cutting edge 28. The cuttingedge 28 limits the flute land 24 to the cutting side of the flute blades22. The thickness of the cutting edge 28 may lie between 0.10 mm and0.40 mm. A cutting edge thickness in the aforementioned range isbeneficial for the cutting efficiency of the drill bit 2.

The thickness of the flute blades 22 may vary along the drill bit 2, inparticular along the longitudinal axis X of the drill bit 2. This allowsfor optimizing the thickness distribution of the drill bit 2 regardingthe force and torque of the drill bit 2. The thickness of the drillflutes may be between 0.8 mm and 1.2 mm.

The second part 8 of the drill tip 2 includes a helix angle δ of between24 degrees and 26 degrees, in particular a helix angle δ of essentially25 degrees, between the longitudinal axis X and a plane of the fluteblades 22. Said range of helix angles δ may be beneficial regarding thebone chip removal and the feed rate of the drill bit 2.

FIGS. 5A and 5B show a cavity or a recess drilled into a skull in aschematically cross-sectional view. The cavity 30 in FIG. 5A drilled isdrilled by two drill bits according to the state of the art. Initially,a first drill is used in order to generate a first cavity 32.Afterwards, a widening drill is used in order to widen the first cavityor recess 32 and to drill a wider cavity 34, thus preparing the cavityor recess 30 for the implant for a bone anchored hearing aid. By usingdifferent drills, the operation surgery time is prolonged and theswitching, restarting and realigning of the widening drill may causeadverse consequences for the cavity or recess to be drilled. The cavity36 may be drilled in one step by using the drill bit 2 according to thepresent disclosure. Hereby, aforementioned disadvantages may be avoided.

FIG. 6 schematically illustrates a guiding tool 38 according to anembodiment of the disclosure in a perspective view. The guiding tool 38preferably is part of a drill kit comprising the drill bit 2 and theguiding tool 38. The guiding tool 38 may protect the soft tissue duringdrilling, ensuring that the correct drilling depth is obtained (thuspreventing too deep cavities 36) and contributing to adequate flushing.In addition, the guiding tool 38 may ensure that the cavity 36 is madeperpendicular to the bone and/or skin surface.

The guiding tool 38 comprises a hollow tube 40 with an external threadedportion 42 for fixating the guiding tool 38 into the operational site byscrewing the guiding tool 38 into the soft tissue. The guiding tool 38further comprises a portion 44 with an enhanced width, wherein theportion 44 with an enhanced width may act as a mechanical stop for theat least on drilling bit 2. The portion 44 is limited by twoperpendicular flanges 46 which can be used in order to manipulate theguiding tool 38.

The diameter of the hollow tube 40 may vary in order to support thedrill bit 2 and to provide space for irrigation room for irrigation orfor a coolant inside the hollow tube 40. FIG. 7 schematically shows across sectional view of a guiding tool 38 according to an embodiment ofthe disclosure. The guiding tool 38 has a hollow tube 40 comprising avarying inner diameter. The hollow tube 40 comprises one upper part 48comprising a first inner diameter, one lower part 52 comprising a secondinner diameter and one middle part 50 located between the upper and thelower part. The inner diameter of the middle part 50 is variable inorder to connect the upper part 48 to the lower part 52. In the hollowtube 40 shown in FIG. 7, the first inner diameter of the upper part 48is smaller than the second inner diameter of the lower part 52.

FIG. 8 schematically shows a guiding tool 38 according to an embodimentof the disclosure in a front view. The guiding tool 38 comprises ahollow channel 56 connected to the hollow tube 40 in order to provide acoolant or saline to the bottom of the osteotomy. The hollow channel 56may be arranged essentially perpendicular to the hollow tube 40 for thedrill bit 2.

FIGS. 9A, 9B and 9C schematically show an implantable fixture screw unit60 configured to receive a bone conduction hearing aid system. Theimplantable fixture screw unit 60 may comprise an elongated part 62where a first end of the elongated part is threaded 63 and configured tobe anchored in the skull bone of the recipient via the drilled cavity orthe recess in the skull. The elongated part 62 may comprise a second endconfigured to receive a skin abutment unit (64, 64A, 64B) configured toreceive the bone conduction hearing aid system. The variation in skinthickness in patients is addressed by the skin abutment unit (64, 64A,64B) of different lengths.

The skin abutment unit 60 may be attached to the elongated part byscrewing (64A) it on to the elongated part or by a snap coupling (64B)where the skin abutment unit (64, 64A, 64B) is pressed on to theelongated part 62 by a movement along an axis orthogonal to the skull.

FIGS. 10A and 10B illustrate further examples of the implantable fixturescrew unit 60. The implantable fixture screw unit 60 include two or moreof the elongated parts (62A, 62B), where the unthreaded part of theelongated part (62A, 62B) is made of an elastic material. In FIG. 10A,the elongated part (62A, 62B) is straight, and in FIG. 10B, theelongated part (62A, 62B) is either trapeze shaped or tapered. In afurther example, the two or more elongated parts may be of the same ordifferent shape. In The diameter of the unthreaded part (62A, 62B) issmaller than a diameter of the threaded elongated part 63. The diameterof the unthreaded part (62A, 62B) of the elongated part is smaller thana diameter of the skin abutment unit (64, 64A, 64B).

The bone conduction hearing aid system may be configured to be connectedto the two or more elongated parts (62A, 62B) either directly onto theskin abutment unit (64,64A,64B) or via an adapter unit 65. FIGS. 11A to11C illustrate an example of the adapter uniter 65. The adapter unit 65is configured to interconnect the two or more elongated parts (62A, 62B)on a first surface 67 of the adapter unit 65 and to connect to the boneconduction hearing aid system 70 on a second surface 66 of the adapterunit 65, and wherein the first surface 67 is opposite to the secondsurface 66, see FIG. 11B. Instead of having a skin abutment unit(64,64A,64B) connected to each of the two or more elongated parts, itwould be of an advantage to interconnect the two or more elongated parts(62A, 62B) with the adapter unit 65 and without the skin abutment unitsbeing connected to the two or more elongated parts, see FIG. 11B.Thereby, the distance from the skin surface to the bone conductionhearing aid system applied onto the implantable fixture screw unit isreduced.

It is intended that the structural features of the devices describedabove, either in the detailed description and/or in the claims, may becombined with steps of the method, when appropriately substituted by acorresponding process.

As used, the singular forms “a,” “an,” and “the” are intended to includethe plural forms as well (i.e. to have the meaning “at least one”),unless expressly stated otherwise. It will be further understood thatthe terms “includes,” “comprises,” “including,” and/or “comprising,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. It will also be understood that when an element is referred toas being “connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element, but an intervening elementmay also be present, unless expressly stated otherwise. Furthermore,“connected” or “coupled” as used herein may include wirelessly connectedor coupled. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. The steps ofany disclosed method are not limited to the exact order stated herein,unless expressly stated otherwise.

It should be appreciated that reference throughout this specification to“one embodiment” or “an embodiment” or “an aspect” or features includedas “may” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the disclosure. Furthermore, the particular features,structures or characteristics may be combined as suitable in one or moreembodiments of the disclosure.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Reference to an element in the singular is not intendedto mean “one and only one” unless specifically so stated, but rather“one or more.” Unless specifically stated otherwise, the term “some”refers to one or more.

Accordingly, the scope should be judged in terms of the claims thatfollow.

1. A drill bit for drilling a cavity or a recess into a skull, whereinthe cavity or the recess is configured to receive an implantable fixturescrew unit of a hearing aid system, the drill bit comprising: a firstpart including a drill tip with a first drill diameter, wherein thedrill tip comprises a tip angle of between 137 degrees to 143 degreesalong a longitudinal axis of the drill bit and wherein the drill tipcomprises a back rake angle of between −1 degree and +1 degree, inparticular a back rake angle of substantially 0 degrees, a second partincluding a plurality of flute blades with a second drill diameter,wherein the second drill diameter is greater that the first drilldiameter, and a transition part which is arranged between the first partand the second part and along the longitudinal axis, wherein thetransition part includes a body clearance.
 2. The drill bit according toclaim 1, wherein each of the plurality of flute blades of the secondpart comprises at least one land, and wherein the second part comprisesparabolic or essentially parallel opposing surfaces extending betweenthe lands of the plurality of flute blades.
 3. The drill bit accordingto claim 1, wherein the plurality of flute blades comprises a cuttingedge with a thickness of between 0.10 mm to 0.40 mm.
 4. The drill bitaccording to claim 1, wherein drill flutes are arranged between theadjacent flute blades and wherein the thickness of the drill flutesvaries along the drill bit and/or wherein the thickness of the drillflutes is between 0.8 mm and 1.2 mm.
 5. The drill bit according to claim1, wherein the second part or the transition part includes a back-rakeangle which is either positive or negative and/or wherein the back rakeangle of the flute blades is within an angle range of between −3 degreesto +3 degrees not including 0 degrees.
 6. The drill bit according toclaim 1, wherein the second part includes a helix angle between thelongitudinal axis and a direction of the flute blades of between 20degrees and 30 degrees, in particular a helix angle of between 24degrees to 26 degrees.
 7. The drill bit according to claim 1, whereinthe transition part includes a region with an essentially constantdiameter along the longitudinal axis and/or wherein a length of theregion with constant diameter along the longitudinal axis is between1.05 mm and 1.55 mm and/or wherein the region with constant diameterdoes not have a cutting edge.
 8. The drill bit according to claim 1,wherein the body clearance includes a minimum diameter equal to aminimum diameter of the first part and a maximum diameter equal to adiameter of the second part.
 9. The drill bit according to claim 1,wherein the body clearance includes a transition angle of 7 degrees to13 degrees along the longitudinal axis and between a minimum diameterand a maximum diameter of the transition part.
 10. The drill bitaccording to claim 1, wherein the length along the longitudinal axis andbetween the end of the drill tip and a maximum diameter of thetransition part is between 4.65 mm and 4.75 mm.
 11. The drill bitaccording to claim 1, wherein the drill tip has a first drill diameterof between 3.78 mm to 3.82 mm and/or wherein the drill tip comprises acutting edge angle of between 7 degrees to 13 degrees.
 12. A drill kit,comprising a drill bit according to claim 1, wherein the drill kitfurther comprises a guiding tool, wherein the guiding tool comprises ahollow tube, and wherein the diameter of the hollow tube is greater thanthe second drill diameter.
 13. A method for drilling a cavity or arecess into a skull, wherein the cavity or the recess is configured toreceive an implantable fixture screw unit of a hearing aid system,wherein the method comprises: applying an incision hole to a bone layerof the skull by using a first tool, cleaning the incision hole by usinga cleaning tool, arranging a guiding tool into the cleaned incisionhole, wherein the guiding tool includes a hollow tube, applying a drillbit into the hollow tube and drilling the cavity or the recess in asingle step.
 14. The method according to claim 13, wherein the drill bitcomprises: a first part including a drill tip with a first drilldiameter, wherein the drill tip comprises a tip angle of between 137degrees to 143 degrees along a longitudinal axis of the drill bit andwherein the drill tip comprises a back rake angle of between −1 degreeand +1 degree, in particular a back rake angle of substantially 0degrees, a second part including a plurality of flute blades with asecond drill diameter, wherein the second drill diameter is greater thatthe first drill diameter, and a transition part which is arrangedbetween the first part and the second part and along the longitudinalaxis, wherein the transition part includes a body clearance, and whereinthe guiding tool is a guiding tool that comprises a hollow tube, andwherein the diameter of the hollow tube is greater than the second drilldiameter.
 15. The drill bit according to claim 2, wherein the pluralityof flute blades comprises a cutting edge with a thickness of between0.10 mm to 0.40 mm.
 16. The drill bit according to claim 2, whereindrill flutes are arranged between the adjacent flute blades and whereinthe thickness of the drill flutes varies along the drill bit and/orwherein the thickness of the drill flutes is between 0.8 mm and 1.2 mm.17. The drill bit according to claim 3, wherein drill flutes arearranged between the adjacent flute blades and wherein the thickness ofthe drill flutes varies along the drill bit and/or wherein the thicknessof the drill flutes is between 0.8 mm and 1.2 mm.
 18. The drill bitaccording to claim 2, wherein the second part or the transition partincludes a back-rake angle which is either positive or negative and/orwherein the back rake angle of the flute blades is within an angle rangeof between −3 degrees to +3 degrees not including 0 degrees.
 19. Thedrill bit according to claim 3, wherein the second part or thetransition part includes a back-rake angle which is either positive ornegative and/or wherein the back rake angle of the flute blades iswithin an angle range of between −3 degrees to +3 degrees not including0 degrees.
 20. The drill bit according to claim 4, wherein the secondpart or the transition part includes a back-rake angle which is eitherpositive or negative and/or wherein the back rake angle of the fluteblades is within an angle range of between −3 degrees to +3 degrees notincluding 0 degrees.